The present invention relates to ambulatory health monitoring and, more particularly, to lightweight wheeze detection methods and systems designed to improve portable respiratory health monitoring devices.
Wheeze monitoring is an important aspect of chronic respiratory disease management, such as asthma management. Wheezes are adventitious lung sounds that are superimposed on normal breath sounds and indicate constricted breathing. A wheeze is generally characterized by a high pitch sound lasting a predetermined duration, and can be detected by evaluating time and frequency components of a respiratory signal.
In conventional wheeze monitoring, a complete short-time Fourier transform (STFT) image is calculated to detect wheezes in a respiratory signal. The complete STFT image provides a two-dimensional representation of the amplitude of the respiratory signal for all data points in a time and frequency domain according to the well-known formula
            STFT      ⁢              {                  x          ⁡                      (            t            )                          }              ≡          X      ⁡              (                  τ          ,          ω                )              =            ∫              -        ∞            ∞        ⁢                  x        ⁡                  (          t          )                    ⁢              w        ⁡                  (                      t            -            τ                    )                    ⁢              ⅇ                              -            j                    ⁢                                          ⁢          ω          ⁢                                          ⁢          t                    ⁢              ⅆ        t            where w(t) is the window function, x(t) is the signal to be transformed and X(τ,ω) is the Fourier transform of x(t)w(t−τ), a complex function representing the phase and magnitude of the signal over time and frequency. Wheezes can be detected from evaluation of selected data points in the complete STFT image.
Conventional wheeze monitoring is not well-suited for portable respiratory health monitoring devices that continually acquire and evaluate a respiratory signal as a person wearing the system goes about his or her daily life. Such devices have limited computing resources, and calculating a complete STFT image to detect wheezes often consumes an unacceptably large share those scarce resources.